


The Darkest Part of her Soul

by zaffrin



Category: Doctor Who (2005)
Genre: Alternate Universe - Daemons, Consensual Daemon Touching, Daemon Feels, F/M, Koschei/the Master is her daemon, Other, daemon AU, is a tag apparantly, that fits
Language: English
Status: Completed
Published: 2021-01-31
Updated: 2021-01-31
Packaged: 2021-03-18 01:47:52
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,908
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29110305
Author URL: https://archiveofourown.org/users/zaffrin/pseuds/zaffrin
Summary: Her daemon looks up at her as she steps inside, and lets the heavy iron door bang back into place, the locks engaging with a click. He is lounging on the sofa across the room, sleek black form stretched out, one paw dangling off the end and yellow eyes watching her silently. His tail twitches, and the Doctor swallows and steps forward.“Hello Koschei.”“Hello traitor,” he replies evenly.
Relationships: The Doctor/The Master (Doctor Who), Thirteenth Doctor/The Master (Dhawan)
Comments: 4
Kudos: 31





	The Darkest Part of her Soul

**Author's Note:**

> IMPORTANT: This is a daemon AU where the Master is the Doctor's Daemon. If you haven't heard of daemons (although who hasn't) perhaps a quick google before you decide whether this is something you want to read. This fic contains sex between the Doctor and her daemon who takes the form of a black panther in this fic, so tentative bestiality warning? Although not really because he's not an animal?? It's complicated but here's your warnings anyway. 
> 
> This fic was inspired by Getting To Know Yourself by TheseusInTheMaze, link at the end :)

  
  
  


Her daemon looks up at her as she steps inside, and lets the heavy iron door bang back into place, the locks engaging with a click. He is lounging on the sofa across the room, sleek black form stretched out, one paw dangling off the end and yellow eyes watching her silently. His tail twitches, and the Doctor swallows and steps forward. 

“Hello Koschei.” 

“Hello traitor,” he replies evenly.

She gives a sigh and runs a hand through her hair. 

“Can we not do this today? It’s been… a long one.”

“Oh, it's been a long day, has it?” He replies as she approaches. “Running about out there, footloose and fancy free? Try spending every minute of it in this infernal prison.”

“Koschei,” she groans. She shoves his tail out of the way, flopping down on the sofa beside him and pressing the heels of her hand to her eyes. “Please. Not today.”

He gives an irritated sigh, and is quiet a minute, clearly having decided to give her the silent treatment. But his curiosity and the way he was wired inescapably to be sensitive to her moods must eventually burn too strong, for he breaks it again after just a moment. “Why not today, particularly?”

“Long story,” she mumbles.

Koschei rolls onto his back, wriggling against the cushions. His back legs kick out, landing in her lap - one across her legs, the other brushing her belly. He kicks at her until she tuts and takes her hands from her face to grab his back foot.

“I’ve got nothing but time,” Koschei drawls when she looks over at him. 

The Doctor gives a sigh, and her hand drifts to his belly, fingers curling into his fur, scratching him idly. He wriggles happily, burrowing into the sofa cushions, and starts to purr at her touch. Things may be…  _ bad _ between them - but he is still her daemon, and closeness like this comes as easily as breathing to the two of them. The Doctor feels herself grow calm as she pets him, relaxation seeping into her bones until the weight and stresses of the day mean little here in Koschei’s presence. 

He gets up after a moment, still purring loudly, and turns round on the sofa to slink over to her, sprawling half across her lap instead, rolling on his back as he looks up at her with glowing yellow eyes.

“Koschei,” she complains, pushing at him. He doesn’t budge. “You’re  _ heavy  _ this time around.”

Koschei himself had been delighted when they had regenerated and he had gone from the small spotted wildcat he (she’d) been in his last form into a large, sleek black panther. The Doctor thinks he is beautiful - she always does. Beautiful and terrible… 

He would have looked startling slinking around next to her. Huge and dark and imposing where she was small and blonde in her brightly coloured outfit. Perhaps that’s why she had chosen it; a constant rebellion against all that Koschei and that part of her soul was. 

His current form fitted him visually perhaps the best of them all so far, and the attitude to go with it. He was a little more unpredictable than last time - just as likely to take a swipe at her with terrifying claws as he was to curl up in her lap… but she didn’t hate it. She didn’t hate him - she  _ couldn’t _ . He was her daemon, a half of her soul… even if it had split in two very different ways. 

It seems he is definitely in one of his more affectionate moods today. When she wriggles out from under him and twists sideways to collapse back on the sofa, shoving at him with her feet, he simply gets up and crawls up over her, flopping down half on top of her, great black body curled around her own. 

“You don’t fit on here anymore,” she complains, pushing at him. He gives a growl, nipping her hand until she gives in and leaves him be. She throws an arm up over her eyes, letting herself fall quiet, listening to the sounds of Koschei’s purring, and his two hearts, beating in time with her own. 

“So, are you going to tell me what’s wrong?” He finally drawls, and the Doctor sighs. 

Mellowed by his closeness, she finds herself relenting. “Just had… a difficult trip. Made some mistakes. Nearly got my friends killed,” she mumbles. 

Koschei gives a scoff. “I don’t know why you always drag humans around with you anyway - I’ve always told you. They’re a liability.”

The Doctor removes her arm to frown at him. “They’re my  _ friends _ .”

“Inferior life forms cannot be friends.” He grins at her then, showing his gleaming white teeth. “Or do you really miss having me at your side so much you had to replace me with the first animals you could find?”

She shoves him, catching him off guard enough to topple him off balance, and he lands on the floor with a thud and a yowl. He hisses at her, getting to his feet and pushes his face right into hers, yellow eyes locked onto her own. 

“What’s wrong love, truth hurts?” He snarls. 

“No,” she replies, and pushes his face away with her hand, sitting up. “They’re not  _ animals.  _ And I don’t miss you.”

“Yeah right,” Koschei snorts. He hops back up onto the sofa next to her, but is content to flop down beside her this time, one giant paw hanging off the edge, tail swishing. “I can feel it, you know. The other half of the ache of separation. Every agonising second of it. And still you insist on keeping me locked in here.”

The Doctor takes a deep breath through her nose, determined not to get drawn into  _ this _ argument again.

“I miss your presence, yes,” she replies as calmly as she can. “Of course I do. But I don’t miss the things you did - the things I had to stop you from doing -  _ constantly -  _ the fear of who you’d hurt next…”

“Oh you’re so _ dramatic, _ ” Koschei rolls his eyes, flopping onto his side and kicking his back feet out so one of those legs dangles off the edge too. 

“And you’re mad,” she shoots back coldly. “You’re my daemon, and it's my responsibility to keep the universe safe from you.”

He snorts. “That’s rich, coming from you.”

“What do you mean?” She frowns. 

“Well.” Koschei rolls onto his back, looking up at her upside down. “You were the one who made me like this, after all.”

She freezes, her blood running cold. 

“You know what they say,” he continues, “that fucking one’s own daemon turns them mad.”

Her chest clenches tight.. “I was barely old enough to know what we were doing!” She hisses. 

He scoffs. “We’re the same age, love.  _ Literally.  _ And you knew well enough to roll onto your belly for me and beg for it, didn’t you?”

She gasps, tears choking her at his words. He’d been a wolf in his first form, and he was right; the Doctor had taken his cock and his knot as readily as he’d offered it… she’d known it was wrong, somewhere in the back of her mind - but instinct was stronger, the need to be as physically close to Koschei as they were emotionally overriding all else. She and her daemon always had seemed to share a different bond to others - deeper. More… ancient, somehow. 

Perhaps it  _ had  _ been what turned him mad… but the Doctor still doesn’t know if she believes that. Koschei was a part of her - and she had fought that darkness inside her from long before the first time they’d been close in that way. 

Koschei was always the personification of that darkness. The voice that goaded her to do things that were selfish, wrong… making her skip out on her classes when they were young, goading her to steal from the library - he had helped her to roll a body into the river when they were barely adolescents - it had been a horrible accident, but Koschei had shown none of the remorse she carried. He’d told her to steal a police box and run away, and she had done it… She thinks perhaps his fate was always inevitable. Still, the first time she’d seen him kill, a little piece of her soul had been ripped from her chest and crushed. She will never forget that day; the gleam in his eyes, the growl that had left his throat, the way he’d looked up at her afterwards, snout and teeth dripping with blood and  _ smiled _ at her like she’d be proud… some nights, she still awoke in a cold sweat to that image. 

He’d become worse from there, his deeds getting darker, the ripples of his destructiveness flowing out further every time, the Doctor getting weaker and weaker at stopping him, until finally, together they had destroyed their entire race. 

It had been for the greater good; to end a horrible, eternal war. That’s what she had told herself. But the delight Koschei had emanated when they watched their whole planet burn to ash put the lie into that claim. 

After then, she had no choice. No choice but to lock him away. It was the hardest thing she had ever done - to keep him trapped. Keep herself physically separate from her daemon, to go about her life without him by her side… but it was the only way. Koschei had been getting stronger, and the Doctor was exhausted with fighting him and that part of herself. He had already killed so many, and she couldn’t let him hurt anyone else. 

In the present, Koschei has leant in, and licks at her face, his long, rough tongue dragging over her cheek, lapping up the salt of her tears. 

“Don’t cry love,” he purrs, a sharp, spiteful edge to his words as his paws flex where they are braced on her thigh, claws digging in. 

“Get off,” she mumbles, shoving at his huge head with her hand, wiping her face with the back of the other. “I don’t know why I bother coming here.”   
She moves to stand, but Koschei moves faster, pinning her with his weight. “Because you can’t keep away. Your soul aches for mine just as mine does for yours. We are two halves of one, after all.”

“I’m nothing like you.”

Koschei smiles, his yellow eyes gleaming, face right up in her own. “Aren’t you?”

She can’t meet his eyes, and judging by the amused chuckle he gives as he nudges his nose into her neck, she knows he’s taken that for her answer. She’s angry at him for his cruel words, and she should push him away again; get up and leave him to his misery and his cruelty alone… but the Doctor’s whole body is relaxing at being close to his like this, and she finds a hand drifting up to scratch him gently round the neck where she should have shoved him away, the other dropping to rest on top of one of his massive paws, still braced on her thigh. 

He purrs as she fusses him, and begins to knead at her thighs. His claws dig in a little, but she doesn’t mind, sighing as she feels the energy being apart from him drains from her form start to recharge, the tension leaving her bones and muscles. 

“You smell good this time around,” he mumbles, sniffing by her collarbone. She gives a shiver at the brush of his cold nose on her skin. 

“I always smell good.”   
“You do,” he agrees, “But it’s different. I like it.”

The Doctor turns her own head and inhales deeply in the ruff of his neck. 

“You smell good too,” she murmurs. It’s a mixture of fur and warmth and  _ home.  _ Koschei. She curls her fingers into his fur then runs her hand down his great strong, sleek back. He is all muscle beneath his shining coat, and it sends a shiver of something else through her form that she tries to ignore. 

Koschei has wriggled even closer to her on the sofa, and he’s pawing at her coat now, pulling aside the collar so he can continue to nuzzle at her skin. 

“Take your clothes off for me love,” he purrs, and there’s a leer on his face - it may not be human but she can see it clear as day in the glint to his yellow eyes and curl of his black lips.

She snorts. “No thanks,” she replies dryly, even as heat curls down her spine and her hearts beat a bit faster. He’d feel it too, the bastard. Her excitement no doubt as tangible to him as his thick lust is to her. It sits, hot and heavy and invasive on the fringes of her consciousness and she swallows hard, trying to shove it all away.

“Oh come on,” he persists, “I haven’t even seen you properly like this yet. Hardly seems fair when you see all of me all the time.”

“That’s different,” she huffs. 

“No it isn’t.”

“ _ Koschei.” _

He leans in closer, nipping her cheek as he gives an irritated growl. “I told you not to call me that.”

The Doctor snorts. “Well I’m hardly going to call my own daemon  _ Master _ .”

“Why not?”

“Because.”

“Because isn’t an answer.”

Somehow - and she isn’t certain how - Koschei had managed to get her to shrug her coat off her shoulders while they were bickering. He’s at her braces down, dragging them off her shoulders with his teeth and his claws, being careful not to scratch her skin. 

“Why am I letting you do this?” She huffs out as she slips her arms free. 

“ _ Because _ …” Koschei tells her, and plucks her shirts carefully from her trousers with his teeth before looking back up at her smugly. “You need me just as much as I need you.”

Tired of him pawing at her, the Doctor yanks her shirts over her head, leaving her hair a mess, and unbuttons her trousers, lifting her hips to shove them and her underwear down and off her legs. When she flops back, she is as bare as her daemon, his fur against her skin as she lets him crawl on top of her. 

“It doesn’t have to be  _ this _ way,” she mumbles, tipping her head back as Koschei nuzzles her neck. 

“Yes it does,” he whispers. 

His fur is soft and warm against her bare skin, and it makes her feel calm as he settles over her, the kind of contentment that can only come from having one's own daemon so close washing over her. It was wrong - but it was them. It had  _ always _ been them. She had already given up so much to try and be good - she spends every minute walking around feeling like half of her was missing, hurting deep inside at being physically separate from him - she couldn’t give up this too. 

His flanks are silky against the inside of her thighs when she parts her legs, lifting them to let him settle between them, linking her heels behind him as if to keep him locked close to her. His purring is loud in her ear, and she can feel his cock, hot and sticky as it bumps against her, and her body arches up in response. 

“I love that you always save your first times for me,” Koschei murmurs. 

“How do you know it’s my first time?”

“Please,” he scoffs. “I would have felt it if you’d fucked someone else. And you always  _ reek _ after you’ve been anywhere near humans like this. I don’t know how you can stand it.”

She huffs, rolling her eyes. “Just hurry - please?” She says instead of arguing. She’s hopeful he’ll think she’s annoyed about the human jab and eager to change the subject, but she knows he’s likely to pick up on how desperately her body aches for his. The dark chuckle he gives into her neck confirms her theory. He moves up, bracing himself on his huge paws either side of her head as he looks down into her face. He looms over her like a shadow like this. Great, black and fearsome, engulfing her very being in his darkness, and the Doctor tries not to reflect on the fact that that darkness wraps around her like a comforting blanket, a shiver going down her spine. 

“Turn over,” he tells her. The request is soft, spoken with the sincerity of him asking for what he wants rather than a desire to dominate her in that moment, and she acquiesces easily, untangling her legs from around him to shift over on the sofa so she’s on her stomach. 

Her heart beats fast, and her cunt burns with anticipation as Koschei leans down and swipes his tongue over the length of her spine from the middle of her back to her neck. A full body shudder goes through her, and she shifts up onto her knees, raising her hips for him. 

“You want me?” He purrs, and then he’s licking back downwards. The Doctor nods against the cushions. 

“You know I do.”

He reaches her lower back, and he’s shifting, moving backwards. When he laps at her again it is directly between her legs, and the Doctor gasps, fingers curling into the sofa cushions at the sensation of his rough tongue dragging through her folds. 

His delight and pleasure at her taste rolls through her, and it makes a fresh wave of desire rush from her, and has she ever been this wet so far? She doesn’t think so. She can feel it leaking from her, sliding down the inside of her thigh as Koschei’s tongue delves into every crevice, mapping out the new shape of her most intimate parts. 

“Please,” she gasps quietly as the rough flat of it drags over her aching clit. 

“Please?” Koschei murmurs against her, and he’s purring now, loudly, the vibrations rumbling through her as he presses his huge open jaws to her and tongues at her. She daren’t move with his great sharp teeth so precariously close to her like this. (She hates that she loves that - that it makes her grow impossibly wetter still, makes lust roll through her hot and thick as boiled syrup). 

“Please,” she puffs out with a shaky exhale. 

“I’ll give you what you want,” He rumbles against her, and nips gently at her sticky inner thigh. “If you give me what  _ I _ want _.” _

Blinking rapidly, confusion oozing through her lust-addled brain, the Doctor twists her neck to try and see him behind her. 

“What do you want?”

Koschei crawls up over her again, his fur soft against her bare back, his body hot as it settles over hers. His cock is hotter still, bumping clumsily between her legs, and she can smell the scent of her own arousal as he brings his mouth close to her face, traces his huge tongue around the shell of her ear. 

“Call me by my name,” he breathes into it. 

She inhales sharply, a small knot of dread dropping into the pit of her stomach. 

She doesn’t answer immediately, and he doesn’t ask again, simply holds himself there, on top of her, his great black form hunched over her own, his breathing hot and loud in her ear. He shouldn’t have this much power over her. It wasn’t how it was supposed to be - he was  _ her _ daemon. A part of  _ her _ . An extension of her own soul… but Koschei’s will had always been strong, and the Doctor’s bond to him too tight for her to deny him.

The Doctor releases a shaky breath, and gives her daemon what he wants. 

“Master,” she whispers. 

She feels him give a shudder of delight against her, and his cock bumps against her cunt. 

“Beg your pardon?”

She knows he’s heard her. Still, she utters it again. “Master.”

He nips at her ear, a sharp sting that makes her gasp. “Can’t hear you, love.”

“ _ Master _ ,” she repeats, and he shoves into her, both of them gasping, the Doctor’s eyes rolling back in her head as he buries himself to the hilt, his soft warm body flush against her backside, his breath panting in her ear. He gives a small growl of delight, and the Doctor moans as he begins to move within her, hips snapping into hers quickly, fucking her almost desperately as his nose nudges through her hair, damp with sweat around her neck until his mouth can open over her skin. 

She cries out as he bites down on the back of her neck. He doesn’t hold her hard enough to cause any damage, but the sharp pricks of pain from his teeth in her skin still ricochet through her, forcing her to keep still beneath him, to lay there and take what he gives her, let him fuck her until he is done. 

Like she would have struggled anyway. 

Feeling him inside of her body this way is new, and a great, rolling heat builds quickly between her legs, a pleasure that consumes her as she lays open mouthed, knees and breasts pressed into the cushions, her face turned sideways as she gasps for air, uncaring of the drool that slips from her mouth and dampens the cushion beneath her face. 

Her whole body shakes when the orgasm grips her. It’s the first time she’s come like this, and tears leak from her eyes as she cries out, wave after wave of pleasure crashing through her, all her senses soaked up in everything that the Master is as he comes inside of her. 

_ The Master _ , she realises with a jolt she had thought as she’d finished. He’s still inside of her, but she’s collapsed down flat, her legs splayed and his soft body heavy and hot on top of her. He releases her neck carefully, licking his lips noisily, and the Doctor lets out a shaky breath as she turns her face to the other side, mouth open as she pants beneath him. 

Koschei is purring, and he nuzzles at her face, licking her affectionately. His huge paws knead the sofa cushions either side of her, and the Doctor feels so utterly content she wishes desperately for a mad, fleeting moment that the rest of the universe didn’t exist. 

Just them. 

“You were a good pet for me,” he murmurs.

The Doctor huffs. “Don’t call me that,” she mumbles, too content to be properly annoyed. 

“Don’t pretend you don’t like it.”

Her treacherous body gives a shudder beneath his, her cunt contracting around his cock still nestled inside her in a little aftershock of pleasure that makes her gasp, and he’s chuckling softly into her hair. 

“Say it again,” he purrs and the Doctor gives another soft gasp, shifting beneath him. She knows what he wants. And she shouldn’t give it to him - shouldn’t give  _ in _ to him - he was her daemon. He was her daemon and he was a part of her - not the other way round. Koschei already believed he had too much power over her… perhaps he did. She kept him locked up in here for the good of the universe, but had she really ever tried to keep him locked away from  _ herself _ ? 

Did she want to? 

She takes a breath, and feels his own ghost hot over the back of her neck. 

_ “Master.” _

\--

**Author's Note:**

> Link to the fic which inspired the idea for this: https://archiveofourown.org/works/28665726
> 
> To anyone who did, thanks for reading! I would love so much to know what you thought, I had a lot of fun with playing with canon to make this one and I've been working on it for a while so feedback would be really appreciated!! <3


End file.
